Monitoring and Correcting Students

Dear colleagues,

How do you monitor and correct your students? Do you:
- answer their questions directly?
- ask a classmate to help?
- ask the whole group?
- take notes and write the mistakes on the board?
- ignore mistakes altogether?
- correct them on the spot?
- wait for a specific moment? How do you decide when it is OK to correct?

What are your ideas? Can you give us any specific techniques?